The present disclosure relates to continuous board (e.g., wallboard) manufacturing processes and, more particularly, to an apparatus, system and method for the distribution of an aqueous calcined gypsum slurry.
It is well-known to produce gypsum board by uniformly dispersing calcined gypsum (commonly referred to as “stucco”) in water to form an aqueous calcined gypsum slurry. The aqueous calcined gypsum slurry is typically produced in a continuous manner by inserting stucco and water and other additives into a mixer which contains means for agitating the contents to form a uniform gypsum slurry. The slurry is continuously directed toward and through a discharge outlet of the mixer and into a discharge conduit connected to the discharge outlet of the mixer. An aqueous foam can be combined with the aqueous calcined gypsum slurry in the mixer and/or in the discharge conduit. The stream of slurry passes through the discharge conduit from which it is continuously deposited onto a moving web of cover sheet material supported by a forming table. The slurry is allowed to spread over the advancing web. A second web of cover sheet material is applied to cover the slurry and form a sandwich structure of a continuous wallboard preform, which is subjected to forming, such as at a conventional forming station, to obtain a desired thickness. The calcined gypsum reacts with the water in the wallboard preform and sets as the wallboard preform moves down a manufacturing line. The wallboard preform is cut into segments at a point along the line where the wallboard preform has set sufficiently, the segments are flipped over, dried (e.g., in a kiln) to drive off excess water, and processed to provide the final wallboard product of desired dimensions.
Prior devices and methods for addressing some of the operational problems associated with the production of gypsum wallboard are disclosed in commonly-assigned U.S. Pat. Nos. 5,683,635; 5,643,510; 6,494,609; 6,874,930; 7,007,914; and 7,296,919, which are incorporated herein by reference.
The weight proportion of water relative to stucco that is combined to form a given amount of finished product is often referred to in the art as the “water-stucco ratio” (WSR). A reduction in the WSR without a formulation change will correspondingly increase the slurry viscosity, thereby reducing the ability of the slurry to spread on the forming table. Reducing water usage (i.e., lowering the WSR) in the gypsum board manufacturing process can yield many advantages, including the opportunity to reduce the energy demand in the process. However, spreading increasingly viscous gypsum slurries uniformly on the forming table remains a great challenge.
Furthermore, in some situations where the slurry is a multi-phase slurry including air, air-liquid slurry separation can develop in the slurry discharge conduit from the mixer. As WSR decreases, the air volume increases to maintain the same dry density. The degree of air phase separated from the liquid slurry phase increases, thereby resulting in the propensity for larger mass or density variation.
It will be appreciated that this background description has been created by the inventors to aid the reader and is not to be taken as an indication that any of the indicated problems were themselves appreciated in the art. While the described principles can, in some aspects and embodiments, alleviate the problems inherent in other systems, it will be appreciated that the scope of the protected innovation is defined by the attached claims and not by the ability of any disclosed feature to solve any specific problem noted herein.